1. Field of the Invention
The present invention relates to a system for making covering masks for use in photoengraving and, more particularly, to a system capable of removing a predetermined portion of a light shielding layer from a stripping film, thereby to make a covering mask.
2. DESCRIPTION OF THE RELATED ART
When, for example, a brochure describing a given commodity is to be printed, an original picture for photo-engraving is prepared from a negative (or positive) picture of the commodity. The image of the commodity is usually taken together with the other objects behind it. The covering mask is used to cover the images of the unnecessary background objects. Namely, the covering mask is placed on the negative picture, covering the images of the background objects, and the negative picture is thus copied photographically, thus forming an original picture showing only the image of the commodity.
A stripping film is usually used to make the covering mask. It is made of a transparent film and a light shielding layer formed on the transparent film. The light shielding layer can be stripped off from the film. The covering mask, or partially cut-off mask is made by removing a predetermined portion of the light shielding layer from the stripping film. In order to copy only the image of the commodity, the light shielding layer must be cut accurately along the outline of the necessary image.
Conventionally, skilled labor is used to cut the covering the light shielding layer from the stripping film. The quality of the covering mask depends upon the skill of the person engaged in the process. This process, which is complicated, requires great skill.
There has been recently proposed an apparatus for facilitating this cut-off process. The apparatus includes a digitizer, a projector for projecting enlarged negative images on the digitizer, a tracing means for tracing the outline of a necessary image selected from those projected, a data processing means (such as the personal computer) for processing data supplied from the tracing means and representing the outline of the image and a cutting means for cutting the stripping film in accordance with the data output from the data processing means. The operator moves a cursor of the tracing means thereby tracing the outline of the necessary image.
This apparatus is disadvantageous in the following respects.
(1) When negative images are projected from above onto the digitizer, the projecting light onto the digitizer is shielded by the head of the operator tracing the outline of a necessary negative image to thereby make the outline partially invisible. When they are projected from below onto the projecting glass screen of the digitizer, the outline of the necessary negative image becomes partially blurred because of the thickness of the glass screen, thereby making an accurate tracing operation impossible.
(2) When the negative is once released from the projector, the negative can hardly be located at the same position as before in the projector. This makes a correction difficult. That is, this makes it difficult to change a part of the outline, and the entire tracing process must be repeated again in this case.